This invention relates to optical sensor devices, and, more particularly, to optical sensor devices of the charge storage type having functions of generating a charge corresponding to incident light and of storing this charge in a suitable site. Such devices are known, for example, as CCD photo-sensors, or CCD photo-diodes which are formed by combining CCDs with photo-diodes.
Recently, a remarkable advance in the semi-conductor art has been achieved, so that charge store type optical sensor devices such as CCD photo-sensors and CCD photo-diodes are available at a very low price. Further, these days, attempts are made here and there to utilize such optical sensor devices in a wide variety of optical instruments.
For example, speaking of the field of distance measurement of a target object, it is proposed that doubled images of an object are formed by the base line distance meter type optical system and then optically scanned by a linear type optical sensor device to produce an output signal representative of the amount of relative discrepancy of these two images, from which the object distance is to be recognized, such as, for example, disclosed in Japanese Patent Laid-Open Specification Nos. Sho 51-45556 and Sho 52-153433, and U.S. Pat. No. 4,004,852. In this sort of apparatus, the particular use of the optical sensor device will lead to an increase in the accuracy of measurement of a distance to the object.
Aside from this, speaking of the field of in-focus detection of an image forming optical system for a given object, instead of using, for example, a photoconductive element having non-linear light response characteristics such as CdS or CdSe receptive of an object image formed by said optical system for producing an output signal which is then utilized in detecting the sharpest focus of image, that is, the in-focus condition, it is made possible to use a linear type optical sensor device which is positioned to electrically scan the above described image with the concurrent image scanning output providing a peak envelope from which a condition of sharpest focus of the image. That is, the in-focus thereof is detected, as disclosed in Japanese Patent Laid-Open Specification No. Sho 54-45127 assigned to the applicant of the present invention. Even in this sort of apparatus, by utilizing the optical sensor device the result is that the condition of in-focus of the image forming optical system can be detected with high accuracy.
The theme of this will now be changed. In these fields of distance measurement and in-focus detection, it is known besides the so-called passive type apparatus which utilizes the light emanating from the object itself in performing the distance measurement or in-focus detection to provide a so-called active type apparatus having a light projector incorporated therein in combination with an optical-electronic detector receptive of the reflected light from the object illuminated with the light projected from the projector for producing an output signal representative of the distance to the object, or the sharpness of an object image formed by the optical system. In the latter connection there have been a great number of proposals made.
A typical example of the active type distance measuring apparatus adapted to associate with an automatic distance adjusting system in a photographic camera is disclosed in Japanese Patent Laid-Open Specification No. Sho 49-49625 assigned to the applicant of the present invention, where, for the photoelectric means receptive of the reflected light from the above mentioned target object, use is made of a plurality of photosensitive elements independent of one another and arranged in predetermined base line intervals from the light projector to correspond to respective different object distances. Upon analysis of the condition of output of the photoelectric light receptor means, detection is made of which photosensitive element receives the reflected light from the target object to evaluate the distance to the target object.
According to another feature of this proposal, when the light projector is rendered operative to project light onto the target object, the concurrent outputs of the individual photosensitive elements are memorized in respective condensors. Then, the light projection is interrupted with production of concurrent outputs from the individual photosensitive elements which are compared with those memorized on the individual condensors to obtain differences therebetween through respective differential amplifiers. Upon detection of which differential amplifier produces an effective output, as to which photosensitive element among the above described plurality of photosensitive elements receives the reflected light from the target object is determined, the distance to the target object is recognized.
It will be appreciated that according to this method, it is possible to effectively remove the influence of the other or ambient light than the projection light (that is, the ambient light functions as the disturbing light in this sort of apparatus, causing the accuracy of distance measurement to be considerably lowered). Thus, it may be expected that the accuracy of distance measurement would be improved.
The apparatus of this proposal is, however, associated with many points requiring further improvements. For one point, since the photosensitive elements are made of a photoconductive material such as CdS, and an electrical circuit arrangement includes resistors connected to the respective individual photosensitive elements with their junction points, that is, voltage dividing points connected to the respective memory condensors, while the differential amplifiers are fed at one of their inputs with the memorized voltages from the individual condensors and at their other inputs with the voltages from the individual junction points, as each condensor memorizes the voltage determined by the resistance value of the respective photosensitive element, the intensity of light projected from the light projecting means must be large enough to insure that the output voltage is of satisfactory operating level for detection.
Particularly in application to a small instrument such as a camera whose electrical power source capacity is limited, therefore, many problems are left yet unsolved. Again, along therewith, in a lighting situation where the environment is very bright, when the light projection is interrupted, the concurrent voltage at the above described voltage dividing junction point becomes very high due to the influence of the ambient light. As a result, the level of the noise component is increased with considerable decrease in the output level of the differential amplifier. There will be a high possibility of encountering the photographic situation where the distance cannot be measured. In another situation where the environmental illumination varies to a large extent from a moment at which light has been projected to a moment at which the light projection is interrupted, as no means is provided to compensate for the variation of the environmental illumination, faulty operation will be possible.
An attempt has been made to overcome all the above mentioned drawbacks of the apparatus of the above described proposal by using a charge storage type optical sensor device according to the present invention which will be described later. It has now been found that the features characteristic of the apparatus are further improved.
In greater detail, the charge storage type optical sensor device is constructed from an optical sensing region having, for example, a plurality of photosensitive elements responsive to incident light for generating charges individually and is provided with first and second charge storage regions each having the same number of charge storage elements as that of photosensitive elements in combination with first and second control gate regions positioned between the optical sensing region and the first and second charge storage regions, respectively, to control the transfer of the charges from the optical sensing region to the first and second charge storage regions. Such device is substituted for the above-described photoelectric light receiving means and the memory condensor arrangement, wherein while the above-described light projecting means is pulsed to produce intermittent lights of a constant period, the above-described first and second control gate regions are controlled to permit the transfer of those of the charges produced from each of the sensor elements in the optical sensing region which occur when light is projected from the light projecting means through the first control gate region to the corresponding one of the charge storage elements in the first charge storing region, while those of the charges produced from each of the sensor elements in the optical sensing region which occur when no light is projected from the light projecting means are transferred to and accumulated on the corresponding one of the charge storage elements in the second charge storing region after having passed through the second control gate region. Thus, the first charge storing region stores a succession of charges representative of the reflected light from the target object illuminated with the projection light and the ambient light, and the second charge storing region stores a succession of charges representative of the light coming from the target object illuminated with the ambient light alone, so that in suitable timed relationship, the charges accumulated on the first and second charge storing regions may be read out for each pair of charge storage elements correlated to each other with respect to the individual sensor element in the first and second charge storing regions to produce electrical signals with a difference therebetween being obtained through a respective differential circuit, thereby it being made possible to detect a signal dependent upon only the projected light from the apparatus with a very high accuracy.
Particularly in this case, since the accumulation of the successive charges leads to effect integration and memorization of information, even when the light energy projected is very weak, a signal whose level is high enough to assure accurate detection can be obtained. Therefore, the detection performance of the apparatus as a whole is further improved, and the detectable range is further extended toward further distances. Again, because of the perfect removal of the noise component due to the ambient light, when the environment is very bright, or even when the environmental illumination varies to a large extent on the way, the satisfactory detection performance can be assured. Thus, the intrinsic merit of the apparatus according to this proposal is further improved to always accomplish accurate detection of the distance.
Besides the above, and functioning as this sort of active type of distance measuring or automatic in-focus detecting apparatus, there is also known, for example, an automatic distance detecting apparatus in Japanese Patent Publication No. Sho 52-19091, where using photoelectric light receiving means responsive to incident light for producing an electrical output which varies with variation of said incident light in position on the light receiving surface thereof, after light is projected from the light projecting means onto a target object, two beams of the reflected light from the target object which are incident in a common plane at respective different positions corresponding to the distance to the target object are allowed to alternately impinge upon said light receiving means with production of those of the outputs therefrom which correspond to one of the incident light beams upon comparison with the other outputs which correspond to the other incident light beam to produce a level difference dependent output which is then used to detect the distance to the above-described target object. Further, as proposed in U.S. Pat. No. 3,999,192 to the applicant of the present invention, after light is projected from the light projecting means, the reflected light from the object is received by two photoelectric elements which are arranged so that their boundaries are adjacent to each other after having passed through a movable light modulating means by which the reflected light is brought to incidence at the interface region between the above-described two photoelectric elements. By the position of the above-described light modulating means which occurs when the difference between the outputs of the two photoelectric elements becomes zero, the distance to the object can be measured.
In addition to such automatic distance detecting apparatus, there is known an automatic in-focus detecting apparatus in which the above-described light modulating means is made to cooperate with a photo-taking optical system in such a manner that the condition of in-focus of an object image formed by said optical system can be detected. A charge store type optical sensor device to be described below may even be applied to such apparatus as the photoelectric light receiving means thereof, thereby giving an advantage that the detection performance is further improved.
With regard first to the apparatus proposed in Japanese Patent Publication No. Sho 52-19091, instead of the above-described photoelectric light receiving means, it is possible to use the charge storage type optical sensor device with the above-described optical sensing region, and the first and second charge storing regions each having, for example, only one element in combination with a masking means or an ND filter of continuous variation in density arranged so that the magnitude of charge generated in response to the incident light varies with variation of the incident light in position on the light receiving surface thereof. To effect an equivalent result to that with the alternate impinging of the two beams of the reflected light on the light receiving surface, the first and second control gate regions are alternately pulsed to permit the ones of the charges produced from the sensor element which correspond to one of the two incident light beams to be transferred to and accumulated on the first charge storing region, while the other charges which correspond to the other incident light beam are transferred to and accumulated on the second charge storing region. Then, in appropriate timed relationship, the first and second charge storing regions are actuated to take out the charges stored thereon in the form of electrical signals, and then a difference between the signals is obtained through a differential circuit.
Thus, even in this case, since the successive accumulation of charges leads to effect integration and memorization of information, even when the energy of the projected light is very weak, the output of the photoelectric means serves as a signal of satisfactory level for detection. Therefore, the detection performance of the apparatus as a whole not only is further improved, but also the range of object distances for which the detection is possible is extended toward longer ones. Again, no matter how small the difference between the incident points of the two beams of the reflected light on the light receiving surface of the sensor element may be, there results in an appreciable difference being created between the magnitudes of output of the first and second charge storing regions to facilitate further improvement of the accuracy of detection.
With regard to the latter apparatus proposed in U.S. Pat. No. 3,999,192, the above-described photoelectric light receiving means is substituted for by a charge storage type optical sensor device with the above-described optical sensing and first and second charge storing regions each having, for example, two elements, whereby, while the light projecting means is pulsed to produce intermittent lights of a constant period as has been mentioned in connection with the apparatus in Japanese Patent Laid-Open Specification No. Sho 49-49625, the gating operation of the first and second control gate regions is controlled alternately in synchronism with the frequency of projection of light to permit the charges produced from the individual sensor elements to be transferred to and accumulated on the first and second charge storing regions in separation from each other depending upon whether or not light is projected. Then, in appropriate timed relationship, the charges stored on the first and second charge storing regions are read out for each of the two pairs of charge storage elements related to each other with respect to the individual sensor elements in the first and second charge storing regions, and are then compared with each other to obtain differences through respective individual differential amplifiers.
Upon detection of whether or not the outputs of these two differential amplifiers coincide with each other, it is possible even in this case to effect an equivalent result to that with the apparatus in Japanese Patent Laid-Open Specification No. Sho 49-49625. Moreover, if however a small difference occurs between the amounts of light received by the two sensor elements, the outputs of the two differential amplifiers clearly differ from each other, thus the accuracy of detection is further improved.